1. Field of the Invention
This invention relates to glass manufacturing methods for producing glass with a modified surface, and more particularly to methods of manufacturing glass having a metallic dispersion of predetermined intensity in a surface thereof. The metallic dispersion may be a uniform metallic dispersion developed in the surface of the glass, particularly flat glass which is modified by the introduction of a metallic dispersion into a surface layer of the glass to enhance solar radiation reflection and absorption by the glass thereby reducing the direct transmission of solar radiation through the glass and providing a high visible light reflection from the surface of the glass containing the metallic dispersion.
The invention may also be employed in glass manufacturing methods in which a metallic dispersion of predetermined intensity is introduced into the glass surface in the form of a decorative pattern which may have a different appearance when viewed by reflected and by transmitted light.
2. Description of the Prior Art
Flat glass with a concentration of metal embodied in a surface layer of the glass has been produced by a modification of the float process. In the float process, flat glass in ribbon form is advanced along the surface of an elongate molten metal bath. A body of molten metal, either a pure metal or a metal alloy, has been confined in contact with the upper surface of the ribbon of glass and the surface constitution of the glass has then been modified by passing an electric current through the glass between the molten metal body and the bath to cause migration of metal ions from the molten metal body into the upper surface of the ribbon of glass.
When employing this method with certain molten alloy bodies, for example copper/lead alloy, regulation of operating conditions has enabled the relative proportions of the two elements of the alloy which migrate into the glass surface to be controlled. Metal ions in the glass surface become reduced to metallic form by subsequent exposure of the ion-rich glass surface to the reducing atmosphere which is maintained over the bath in the customary way of operating the float process. A typical atmosphere contains 90% nitrogen and 10% hydrogen.
Other alloys have been employed, for example silver/bismuth alloys, nickel/bismuth alloys, copper/bismuth alloys and nickel/tin alloys. It has also been proposed to employ a pure metal, for example indium, for treating the glass. Usually the molten metal body is located in contact with the upper surface of the advancing ribbon of flat glass by clinging to a locating member which is positioned in the tank structure containing the molten metal bath so as to extend transversely across the path of travel of the ribbon of glass. The locating member may be of elongate rectangular form, and when direct current is passed from the locating member so as to cause ionic flux across the interface between the molten metal body and the glass, a uniform metallic dispersion in the glass surface results. The use of alternating current has been proposed in order to provide treatment of the upper surface from the molten metal body located in contact with that surface and to provide treatment of the lower surface of the advancing ribbon with metal from the molten metal bath.
It has also been proposed to produce shaded characteristics longitudinally of the ribbon of glass, that is in the direction of advance of the ribbon, by continuously varying the voltage applied to the molten metal body and so continuously varying the intensity of surface modification of the glass. Two molten alloy pools have been proposed for carrying out a two-stage treatment of the glass. A reducing agent, for example arsenic may be introduced into the upper surface of the ribbon from the first pool, and metal ions which are to produce a metallic dispersion in the glass, for example copper ions, are caused to migrate into the glass from the second pool and are reduced by the arsenic already present in the glass to give the glass a distinctive colour, commonly, in the case of copper, red. This manner of operating does not rely on reducing properties of the protective atmosphere over the bath to develop colour in the glass surface.
It has further been proposed that a first molten metal body be connected as an anode while a second molten metal body is connected as a cathode so that an element, for example lithium or zinc, migrates into the upper surface of the glass from the first body and the same element migrates into the lower surface of the glass from the molten metal bath supporting the ribbon of glass, in which bath a predetermined concentration of that element is maintained. This produces symmetrical treatments of the glass surfaces, for example lithiumrich glass surfaces which are subsequently employed in a chemical toughening process, or zinc-rich glass surfaces which improve the weathering properties of the glass.
Generally, when uniform modification of the surface of the glass is to be effected, the shape of the area of contact between the molten metal body from which ionic migration takes place and the upper surface of the glass is maintained of rectangular configuration as described above. Because the molten metal or metal alloy clings to the metal bar, the configuration of the area of contact between the molten metal or metal alloy and the glass corresponds to the configuration of the face of a locating member adjacent the glass. Thus patterned float glass may be produced by a method in which the molten metal body is shaped to a configuration progenitive of a pattern to be introduced into the glass and a predetermined ionic migration between the shaped molten body and the glass is engendered in a defined time period which is related to the speed of advance of the ribbon of glass beneath the shaped molten body. The time period is sufficient to produce a pattern element of modified glass in the glass surface which pattern element exhibits its derivation from the configuration of the molten body, and hence from the configuration of the locating member. A repeated pattern is introduced by repeatedly engendering ionic migration in a sequence of defined time periods determined by applying to the molten body an anodic waveform of voltage pulses at spaced intervals defining that sequence of time periods of ionic migration from the molten body into the glass.
In the treatment processes described above, a molten metal or metal alloy body is connected as an anode with respect to the glass to cause migration of metal cations from the molten body into the glass. In practice, the application of the anodic electricity to the molten body may result in partial oxidation of the molten body. Such oxidation may reduce the efficiency of the anodic treatment; loss of efficiency may be particularly acute when a molten indium body is used, but is also significant with other molten metals and alloys, for example molten copper/lead alloys.